Protein kinases are key regulators for cell growth, proliferation and survival. Genetic and epigenetic alterations accumulate in cancer cells leading to abnormal activation of signal transduction pathways which drive malignant processes. (Manning, G.; Whyte, D. B.; Martinez, R.; Hunter, T.; Sudarsanam, S. The protein kinase complement of the human genome. Science 2002, 298, 1912-1934). Pharmacological inhibition of these signaling pathways presents promising intervention opportunities for targeted cancer therapies. (Sawyers, C. Targeted cancer therapy. Nature 2004, 432, 294-297).
The tropomyosin-related receptor tyrosine kinases (Trks) are high-affinity receptors for neurotrophins (NTs), a nerve growth factor (NGF) family. Trk was originally cloned as an oncogene fused with the tropomyosin gene in the extracellular domain. The activating mutations caused by chromosomal rearrangements or mutations in TRK family have been reported in many cancers. (Vaishnavi A, et al Cancer Discov. 2015, 5, 25) Because Trks play important roles in pain sensation as well as tumor cell growth and survival signaling, inhibitors of Trk receptor kinases might provide benefit for pain and cancer treatment.
The Janus family of kinases (JAKs) include JAK1, JAK2, JAK3 and TYK2, and are cytoplastic non-receptor tyrosine kinases required for the physiologic signaling of cytokines and growth factors. (Quintas-Cardama A, et al., Nat. Rev. Drug Discov. 2011, 10(2), 127) Aberrant regulation of JAK/STAT pathways has been implicated in multiple human pathological diseases, including cancer (JAK2) and rheumatoid arthritis (JAK1, JAK3). A gain-of-function mutation of JAK2 (JAK2V617F) has been discovered with high frequency in patients having myeloproliferative neoplasms (MPN). (Levine R L, et al. Cancer Cell 2005, 7, 387) The mutation in the JH2 pseudokinase domain of JAK2 leads to constitutively kinase activity. Cells containing the JAK2V617F mutation acquire cytokine-independent growth ability and often become tumor, providing strong rationale for the development of JAK inhibitors as a targeted therapy. In addition, hyperactivation of the JAK2/signal transducers and activators of transcription 3 (JAK2/STAT3) is responsible for abnormal dendritic cell differentiation leading to abnormal dendritic cell differentiation and accumulation of immunosuppressive myeloid cells in cancer (Nefedova Y, et al. Cancer Res 2005, 65, 9525). In Pten-null senescent tumors, activation of the JAK2/STAT3 pathway establishes an immunosuppressive tumor microenvironment that contributes to tumor growth and chemoresistance (Toso A, et al. Cell Reports 2014, 9, 75). JAK2 gene fusions with the TEL(ETV6) (TEL-JAK2) and PCM1 genes have been found in leukemia patients. (Lacronique V, et al. Science 1997, 278, 5341, 1309-12. Reiter A, et al. Cancer Res. 2005, 65, 7, 2662-7.) It was reported that JAK/STAT3 signaling pathway was aberrantly increased in EGFR inhibitor-resistant EGFR-mutant non-small cell lung cancer (NSCLC) cells, and JAK2 inhibition overcomes acquired resistance to EGFR inhibitors that support the use of combination therapy with JAK and EGFR inhibitors for the treatment of EGFR-dependent NSCLC. (Gao S P, et al. Sci Signal. 2016, 9 (421):ra33) JAKiSTAT3 signaling promotes cancer hallmarks in the tumor and its environment, including proliferation, survival, angiogenesis, tumor metabolism while suppressing antitumor immunity. (Buchert M. et al. Oncogene, 2016, 35, 939-951) Inhibition of cytokine-dependent activation of the JAK/STAT3 pathway with JAK inhibitors may also afford orthogonal treatment opportunities for other oncogene-addicted cancer cells that have gained drug resistance. Focal amplification of JAK2 gene was observed in postchemotherapy triple-negative breast cancers (TNBCs) in a group of 9p24-amplified tumors, suggesting a role in tumorigenicity and chemoresistance. (Balko J M, et al. Sci Transl Med. 2016, 8(334):ra53) Therefore, pharmacologic inhibition of the JAK2 signaling pathway can be an important new therapeutic strategy to enhance antitumor activity.
Bruton's tyrosine kinase (BTK) was originally identified in 1993 as a non-receptor protein tyrosine kinase that is defective in the inherited immunodeficiency disease X-linked agammaglobulinaemia (XLA). (Vetrie D. et al. Nature 1993, 361, 226-233) BTK functions downstream of the B cell receptor, and is a mediator of B-cell receptor (BCR) signaling. BTK plays a critical role in the development, activation and differentiation of B cells (Mohamed A J et al, Immunological Reviews, 2009, 228, 58-73). Abnormal activation of BTK is responsible for aberrant proliferation and homing of various malignant B cells. The irreversible BTK inhibitor ibrutinib was approved for relapsed/refractory chronic lymphocytic leukemia (CLL) & mantle cell lymphoma (MCL), CLL with p17 del and Waldenstrim's macroglobulinemia (WM). Acquired resistance to ibrutinib has been observed in CLL (Furman R R, et al. New England Journal of Medicine, 2014, 370, 2352-2354) and MCL (Chiron D, et al. Cancer Discovery, 2014, 4, 1022-1035) patients due to mutation of C481S required for covalent binding of ibrutinib to the kinase active site. Ibrutinib inhibited the recombinant BTK C481S 25-fold less potently than WT. (Woyach J A, et al. New England Journal of Medicine, 2014, 370, 2286-2294) The loss of covalent binding cysteine leads to ineffective BTK inhibition and ultimately results in ibrutinib resistance. Therefore, the development of reversible ATP competitive BTK inhibitors with comparable activity towards wild type BTK and mutated C481S BTK is necessary to provide an alternative treatment option for patients with acquired resistance to ibrutinib. It was reported that BTK regulates B-cell and macrophage-mediated T-cell suppression in pancreas adenocarcinomas. (Gunderson A J, et al. Cancer Discov. 2016, 6, 270-285) The BTK inhibitor ibrutinib restored T cell-dependent antitumor immune responses to inhibit PDAC growth and improved responsiveness to chemotherapy. In addition to its critical roles in B cell development, Btk also contributes to the activation of the FcγR and FcεR signalling pathways in macrophages, neutrophils and mast cells. Btk is a promising target for therapeutic intervention in autoimmune and inflammatory disease, e. g. rheumatoid arthritis (RA) (Di Paolo J A, et al. Nature Chemical Biology 2011, 7, 41-50) and systemic lupus erythematosus (SLE). (Bender A T, et al. Clinical Immunology 2016, 164, 65-77) The development of reversible and highly selective BTK inhibitors is highly desired for chronic disease treatment.